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3. Color differences in the sexes of a crab. 



By E. A. Andrews, Johns Hopkins University, Baltimore JMd. 

 (Witli 2 figures.; 



eingcg. 25. Januar 1911. 



In Crustacea the male and female may be easily distinguished, 

 generally by differences in form and organization, l)ut not by differences 

 in color. 



The sexes differ not only in the essential organs, testes and ovaries, 

 in the passageways from these organs to the exterior and in the ex- 

 ternal openings, but also, commonly, in many or fewer organs directly 

 concerned with the transfer and reception of sperm and again in the 

 organs concerned in the carrying or- protection of the eggs. Most of the 

 external differences between male and female may be referred to one 

 or the other of these categories; either they relate to the bringing of 

 sperm and egg together or else to the care of the eggs. A marked diffe- 

 rence in the size and shape of the claws is often connected with the 

 mode of sperm transfer and may be so in cases in which at present evi- 

 dence is lacking as to any meaning of the great claws of the male. 

 There remains, in some Crustacea, the differences in size of the entire 

 animal, which may be very striking, yet have no apparent value with 

 reference to sperm transfer or to care of eggs. Here again some more 

 or less direct connection with these necessary acts may be suspected. 



As a rule the sexes in Crustacea have the same coloration, but a 

 few exceptions have been noted amongst the highest forms. Thus 

 Conn, in the J. H. University Circulars, 1883, cites Darwin as know- 

 ing of but two cases of color differences, in Crustacea, Squilla styUfera 

 and a species of Gelasimiis. Conn then describes the remarkable inten- 

 sity and special distribution of blue color on the great claws of the male 

 of another crab, the common Calinectes of the Chesapeake, as con- 

 trasted with the orange color or less brilliant blue of the like parts of 

 the female. 



To these instances may be added the case of the mud crabs, Neo- 

 panope texana (Stimpson) as mentioned by Benedict and Rathbun, 

 Proc. Nat. Mus. XIV. 1891. p. 363—364, in which the finger tip of the 

 claw of the male is lighter than in the female, in a subspecies, but much 

 darker in the type. 



While other cases may" have escaped review the following is suffi- 

 ciently novel to be worthy of notice. 



At Montego Bay, Jamaica, B.W.I, the Marine Laboratory of the 

 Johns Hopkins University found a wealth of crustacean forms and 

 amongst them the large hermit crab, Petrochinis hahamensis (Herbsti 



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